1. Field of the Invention
The present invention relates to conductive pastes and laminated ceramic electronic components, and more particularly, relates to a conductive paste advantageously used for internal electrodes of laminated ceramic electronic components and to a laminated ceramic capacitor using the conductive paste.
2. Description of the Related Art
Heretofore, laminated ceramic electronic components, such as laminated ceramic capacitors, have laminates comprising a plurality of ceramic layers and at least one internal electrode formed along a predeternined interface between the ceramic layers.
In the laminated ceramic electronic components, internal electrodes are generally formed by a step of printing a conductive paste containing a conductive powder and an organic vehicle, which are dispersed in a solvent, and a subsequent step of firing the conductive paste thus printed. In more detail, a laminated ceramic electronic component is formed by steps of printing a conductive paste, which is to be used as internal electrodes, on predetermined ceramic green sheets, which forms ceramic layers by firing; laminating the ceramic green sheets with each other; bonding the ceramic green sheets with each other by compression; and firing the ceramic green sheets bonded together; whereby the internal electrodes are simultaneously sintered together with the ceramic green layers, and a ceramic laminate provided with the internal electrodes is formned. In the steps described above, the melting point of the conductive powder, which forms the internal electrodes, must be not less than the sintering temperature for the ceramic. When the melting point of the conductive powder is less than the sintering temperature for the ceramic, the conductive powder is melted during firing, and breakages may occur in the internal electrode after the firing is performed, resulting in degradation of the coverage. Accordingly, as the conductive powder, Pt, Pd, W, Nb, Ni and the like may be used, and in order to reduce the cost, Ni, which is a base metal, is used as the conductive powder.
In a laminated ceramic electronic component having internal electrodes composed of a base metal such as Ni, concomitant with the trends toward thinner ceramic layers and an increased number of ceramic layers, the following problems may arise. Residual stress remaining at the interfaces between the internal electrodes and the ceramic layers is increased due to the differences in shrinkage, and in coefficient of thermal expansion, caused by sintering the electrode films formed by printing and the ceramic green layers. As a result, a problem may arise in that heat shock resistance of the laminated ceramic electronic component is degraded. In addition, concomitant with the trends toward thinner ceramic layers and an increased number of ceramic layers, another problem may also arise in that the reliability of the laminated ceramic electronic component at a high temperature under a high humidity condition, i.e., so-called high humidity loading characteristics, is degraded.
Furthermore, as the thickness of the ceramic layer is decreased, the thickness of the internal electrode layer must also be decreased, and hence, it is required that the particle size of the conductive powder which is contained in the conductive paste for forming the internal electrode must be further decreased. However, when the particle size of the conductive powder is further decreased, since the shrinkage of the internal electrode which is caused by sintering of the conductive powder during firing occurs at an even lower temperature, a problem may arise in that delamination of the ceramic layers is likely to occur.
In order to solve the latter problem, i.e., the problem of delamination, for example, a laminated ceramic capacitor formed by bonding an internal electrode composed of Ni to a ceramic layer by using an aluminosilicate layer is disclosed in Japanese Examined Patent Application Publication No. 7-56850. However, this laminated ceramnic capacitor does not address the former problem, that is, the problem of poor heat shock resistance.
In addition, in Japanese Unexamined Patent Application Publication No. 8-259847, a conductive paste using powdered metal covered with a reaction product of an organic silicone compound and water is disclosed. However, when this conductive paste is used for forming an internal electrode for a laminated ceramic capacitor, the silicon contained in the conductive paste reacts with the ceramic, and as a result, abnormal grain growth of the ceramic occurs, whereby the former problem, i.e., the problem of poor heat shock resistance, cannot be reduced.
Accordingly, an object of the present invention is to provide a conductive paste which generates no delamination during firing and which has superior heat shock resistance and humidity loading resistance, and to provide a laminated ceramic electronic component comprising internal electrodes formed of the conductive paste described above.
To these ends, a conductive paste of the present invention comprises a conductive powder primarily comprising Ni; an organic vehicle; a compound A comprising at least one material selected from the group consisting of an organic acid metal salt, an organic metal complex salt and an alkoxide, containing at least one element selected from the group consisting of Mg, Ca and Ba; and a hydrolyzed compound B containing at least one of Al and Si; wherein the hydrolyzed compound B is adhered to the surface of the conductive powder.
In addition, a conductive paste of the present invention comprises a conductive powder primarily comprising Ni; an organic vehicle; a compound A comprising at least one material selected from the group consisting of an organic acid metal salt, an organic metal complex salt and an alkoxide, containing at least one element selected from the group consisting of Mg, Ca and Ba; and a hydrolyzed compound B containing at least one of Al and Si; wherein the compound A and the hydrolyzed compound B are adhered to the surface of the conductive powder.
The compound B may comprise a hydrolysable reactive group, and the hydrolysable reactive group is preferably an alkoxyl group.
The compound B may comprise an alkoxide.
The compound B may comprise at least one material selected from the group consisting of an aluminum chelate compound, an aluminum alkoxide, a silane monomer and a silicon alkoxide.
The adhesion amount of the hydrolyzed compound B is preferably about 0.1 to 5.0 wt %, in the form of SiO2 and Al2O3, with respect to 100 wt % of the conductive powder.
The molar ratio of Si, in the form of SiO2, contained in the hydrolyzed compound B to the total of Mg, Ca and Ba, in the form of MgO, CaO and BaO, respectively, contained in the compound A is preferably in the range of about 0.5 to 10.0.
In addition, the molar ratio of Al, in the form of Al2O3, contained in the hydrolyzed compound B to the total of Mg, Ca and Ba, in the form of MgO, CaO and BaO, respectively, contained in the compound A is preferably in the range of about 0.5 to 4.0.
A laminated ceramic electronic component of the present invention comprises a laminate having ceramic layers laminated with each other and internal electrodes provided along predetermined interfaces between the ceramic layers, wherein the internal layers are formed by firing the conductive paste according to the present invention.
In addition, the laminated ceramic electronic component described above may further comprise terminal electrodes provided at different positions on side surfaces of the laminate, wherein the internal electrodes are in electrical contact with the terminal electrodes.
Furthermore, the ceramic layer of the laminated ceramic electronic component may primarily comprise barium titanate.